1. Field of the Invention
The invention relates to a shifting apparatus and a shifting control method thereof. In particular, the invention relates to a normally meshed gear transmission and a shifting control method thereof.
2. Description of the Related Art
There has been known a related art wherein an actuator is used to engage or release a clutch and select a gear stage in a shifting apparatus having a normally meshed gear transmission. In some of shifting apparatuses thus constructed, so-called double clutch control is performed. That is, in switching from one gear stage to another (e.g., in performing downshift), a clutch is temporarily engaged in a neutral state to cause a rise in engine speed, so that input and output shafts of a normally meshed gear transmission will synchronize with each other.
Japanese Patent Application Laid-Open No. 2001-280472 discloses a rotational synchronization device for a transmission which suitably utilizes electronic control to achieve further facilitation. The rotational synchronization device for the transmission disclosed in Japanese Patent Application Laid-Open No. 2001-280472 has a dog gear and a sleeve, and carries out rotational synchronization of a transmission that is electronically synchronically controlled. The dog rear is rotatable with respect to a main shaft and rotates together with a main gear that is driven by an engine via a clutch. The rotational synchronization device of this transmission includes a double clutch control portion that performs double clutch control for raising a rotational speed of the dog gear by temporarily connecting the clutch and controlling rotation of the engine if a rotational speed of the dog gear (a rotational speed of the main gear) in a shifting target gear stage is lower than a rotational speed of the sleeve (a rotational speed of the main shaft) in switching from one gear stage to another, and that prohibits double clutch control if a vehicle runs at a low speed and decelerates.
According to the invention disclosed in this publication, rotational synchronization can be realized by raising the rotational speed of the dog gear to match the rotational speed of the sleeve through double clutch control. For instance, in making a downshift while traveling uphill, if the vehicle is almost on the verge of stopping while running at a low speed that is substantially decreasing, double clutch control is prohibited. If double clutch control is prohibited, rotational synchronization is rapidly carried out with the aid of a decrease in the rotational speed of the sleeve. Hence, the operation of switching from one gear stage to another is rapidly completed, and a feeling of smooth and comfortable shifting can be obtained.
In the rotational synchronization device for the transmission disclosed in the aforementioned publication, if the rotational speed of the dog gear in the shifting target gear stage is lower than the rotational speed of the sleeve during a switch in gear stage when the vehicle is neither running at a low speed nor decelerating, double clutch control is performed. In double clutch control, however, after the clutch has been disconnected, the gear is neutralized to temporarily connect the clutch and raise the engine speed, so that the rotational speeds of the input and output shafts of the normally meshed gear transmission are synchronized with each other. After the completion of synchronization, the clutch is disconnected again to switch from one gear stage to another. Then the clutch is connected again. Namely, the operation of disconnecting the clutch needs to be performed twice. The shifting period in double clutch control is not always shorter than the shifting period in synchro control. Hence, the shifting period is prolonged, and a sense of incongruity resulting from undesired performance of shifting may be conveyed to the driver of the vehicle.